Educators especially: I encourage you to use anything you find here that is useful to your mission educating people about Earth science. E-mail me if it would help to have a larger or higher-resolution version of any of the images.

As with last week’s Friday Fold, this fold owes its existence to (a) deposition of sandstone and shale in the Western Interior Seaway, and (b) deformation under a giant thrust sheet during the thin-skinned compressional tectonics of the Sevier Orogeny.

In this case, we’re south of the Lewis Thrust, and the local equivalent is called the Dorado Thrust. It’s basically the same exact thing you find up north in Glacier National Park: Mesoproterozoic Belt Supergroup metasedimentary rocks thrust as a relatively coherent sheet over weaker, younger Mesozoic sedimentary strata.

The fold is moderately plunging towards the road, which is how I was able to nestle in, tucked into the trough of the syncline, the length of my body parallel to the axis of the fold.